Thermal seal between manifold and nozzle

ABSTRACT

A seal is provided between a nozzle and a manifold. The seal provides a melt channel between an outlet of the manifold and a nozzle channel. The seal has higher thermal expansion coefficient than both the nozzle and the manifold to provide an improved seal between the manifold and the nozzle when the injection molding apparatus is at an operating temperature.

This application claims the benefit of U.S. Provisional Application No.60/353,212 filed on Feb. 4, 2002.

FIELD OF THE INVENTION

The present invention relates generally to an injection moldingapparatus and, in particular, to an improved seal between a manifold anda nozzle.

BACKGROUND OF THE INVENTION

A common problem associated with hot runner injection molding systems isthe leaking of molten plastic that can occur between the manifold andthe nozzle. Leaking is typically caused by operation of the hot runnerinjection molding system outside of the designated operating window.There are many different nozzle designs of the prior art that attempt tostop leakage from occurring.

A pair of spacers located between a manifold and a cover plate or a hotrunner plate, such as disclosed in U.S. Pat. Nos. 6,309,207, 6,062,846and U.S. patent application No. 2001/0011415, apply a contact pressurebetween the nozzle body melt channel and the manifold melt channel toachieve a seal therebetween. The spacers are arranged in series with afirst spacer abutting the manifold and a second spacer abutting thecover plate. The second spacer has a different response characteristicto compressive pressures than the first spacer.

WO 01/87570 A1 discloses a non-flat sealing interface, which is providedbetween a nozzle and a manifold. A spring urges the nozzle against themanifold to produce a pressure distribution with a peak sealing pressurethat occurs adjacent the nozzle and manifold melt channels. SimilarlyU.S. Pat. No. 5,896,640 discloses a sealing insert that abuts a nozzleshoulder. The sealing insert generates an angular sealing force andmaintains sealing contact between the nozzle and manifold channels. Thesealing insert produces a peak sealing pressure that occurs adjacent thenozzle and manifold channels.

It is an object of the present invention to provide a novel thermal sealfor reducing the leakage between a manifold and a nozzle.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided aninjection molding apparatus comprising:

a manifold having a manifold channel, the manifold channel having aninlet for receiving a melt stream of moldable material and an outlet fordelivering the melt stream to a nozzle channel of a nozzle;

a sealing element provided between the nozzle and the manifold, thesealing element including a melt channel for receiving the melt streamfrom the outlet of the manifold channel and delivering the melt streamto the nozzle channel; and

a mold cavity for receiving the melt stream from the nozzle channel, thenozzle channel communicating with the mold cavity through a mold gate;

wherein the sealing element has a higher thermal expansion coefficientthan both the nozzle and the manifold.

According to another aspect of the present invention there is providedan injection molding apparatus comprising:

a manifold having a manifold channel for receiving a melt stream ofmoldable material under pressure;

a manifold plug provided in the manifold, the manifold plug having amanifold plug channel formed therein, the manifold plug channel havingan inlet for receiving the melt stream from the manifold channel and anoutlet for delivering the melt stream to a nozzle channel of a nozzle;and

a mold cavity for receiving the melt stream from the nozzle channel, thenozzle channel communicating with the mold cavity through a mold gate;

wherein the manifold plug has a higher thermal expansion coefficientthan both the nozzle and the manifold.

According to yet another embodiment of the present invention there isprovided an injection molding apparatus comprising:

a manifold having a manifold channel, the manifold channel having aninlet for receiving a melt stream of moldable material under pressureand an outlet;

a nozzle having nozzle body and a nozzle head, the nozzle head beinglocated adjacent an outlet surface of the manifold, the nozzle having anozzle channel for receiving the melt stream from the outlet of themanifold channel; and

a mold cavity for receiving the melt stream from the nozzle channel, thenozzle channel communicating with the mold cavity through a mold gate;

wherein at least a portion of the nozzle head has a higher thermalexpansion coefficient than both the nozzle body and the manifold.

The present invention provides advantages in that the sealing elementprovides a continuous sealed melt channel between the manifold and thenozzle to minimize leakage at the connection therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described more fullywith reference to the accompanying drawings in which:

FIG. 1 is a side sectional view of a first embodiment of an injectionmolding apparatus of the present invention;

FIG. 2 is a side sectional view of parts of an injection moldingapparatus of a further embodiment of the present invention;

FIG. 3 is a side sectional view of the injection molding apparatus ofFIG. 2 in an operating condition;

FIG. 4 is a side sectional view of parts of a further embodiment of aninjection molding apparatus of the present invention;

FIG. 5 is a side sectional view of the injection molding apparatus ofFIG. 4 in an operating condition;

FIG. 6 is a side sectional view of parts of yet a further embodiment ofan injection molding apparatus of the present invention;

FIG. 7 is a side sectional view of the injection molding apparatus ofFIG. 6 in an operating condition;

FIG. 8 is a side sectional view of a further embodiment of an injectionmolding apparatus of the present invention;

FIG. 9 is a side sectional view of the injection molding apparatus ofFIG. 8 in the operating condition;

FIG. 10 is a side sectional view of a further embodiment of an injectionmolding apparatus of the present invention;

FIG. 11 is a side sectional view of a further embodiment of an injectionmolding apparatus of the present invention;

FIG. 12 is a side sectional view of still a further embodiment of aninjection molding apparatus of the present invention;

FIG. 13 is a side sectional view of a further embodiment of an injectionmolding apparatus;

FIG. 14 is a side sectional view of a further embodiment of an injectionmolding apparatus;

FIG. 15 is a side view of a sealing insert of the injection moldingapparatus of FIG. 14; and

FIG. 16 is a cross-sectional view taken along on line A of FIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, an injection molding apparatus is generallyindicated by reference numeral 10. The injection molding apparatuscomprises a manifold 12 having a manifold channel 14 extendingtherethrough. A manifold bushing 16 that is located at an inlet of themanifold channel 14 receives a melt stream of moldable material from amachine nozzle (not shown). The melt stream flows through the manifoldchannel 14 and is delivered to outlets 18, as indicated by the arrows17. Manifold heaters 15 are provided in the manifold 12 to maintain themelt stream at a desired temperature.

Nozzles 20 are located between the manifold 12 and respective moldcavities 30, which are formed in mold cavity plates 35. Each nozzle 20includes a nozzle channel 22 for receiving the melt stream from therespective manifold outlet 18 and delivering the melt stream to therespective mold cavity 30. Mold gates 31 are provided at the entrance tothe mold cavities 30, adjacent tips 24 of the nozzles 20. Each nozzle 20includes a valve pin 21 that is driven by a valve piston 23. The valvepins 21 are selectively movable to open and close the respective moldgates 31. Each nozzle 20 is further provided a heater 40, which helps tomaintain the melt stream at a desired temperature as it passes throughthe nozzle 20. Cooling channels 33 are located adjacent the moldcavities 30 in order to aid in the cooling thereof.

The injection molding apparatus 10 of FIG. 1 further includes a sealingelement or a sealing insert 44 that is located between the nozzle 20 andthe manifold 12. The sealing insert will be described in more detail inrelation to FIGS. 2 to 7. In each of the following injection moldingapparatus embodiments, like reference numerals represent like parts.

Referring to FIG. 2, another embodiment of an injection moldingapparatus 10 a is shown. In this embodiment, a manifold plate 36 abutsthe mold cavity plate 35 a.

A nozzle shoulder 32 is provided at an upper end of the nozzle 20 a. Thenozzle shoulder 32 includes an upper surface 26, which abuts an outletsurface 28 of a manifold 12 a. The nozzle shoulder 32 includes adownwardly directed spacing flange 34 that is supported by the manifoldplate 36.

A backing plate 50 is located adjacent the manifold 12 a and is offsetby a gap 51. A spring 52 is provided between the backing plate 50 andthe manifold 12 a. The spring 52 may alternatively be a rigid spacer.The spring 52 absorbs movement of the manifold 12 a caused as a resultof thermal expansion, which occurs when the manifold 12 a and nozzle 20a heat up to the operating temperature range.

The nozzle 20 a further includes a recess 41 that is formed in an uppersurface 26, or manifold contacting surface, of the nozzle 20 a. Thedepth of the recess 41 is delimited by a shoulder 46. A sealing insert44 a, which is generally a sleeve having a bore 47, is nested in therecess 41. The melt stream flows through the bore 47 from a manifoldoutlet 18 a and into nozzle channel 22 a. The sealing insert 44 a has alength 60 and a wall thickness 62. The wall thickness 62 is typically inthe range of 2 to 3 mm. The sealing insert 44 a and manifold 12 a arearranged so that a cold clearance, indicated at 48, is provided betweenthe sealing insert 44 a and the manifold 12 a.

The sealing insert 44 a has a higher thermal conductivity than both themanifold 12 a and the nozzle 20 a, which are typically comprised of toolsteels such as H13 or P20 steel, for example. The sealing insert 44 amay be comprised of copper, beryllium copper, brass, carbide or somesteels. Alternatively, any suitable material having a higher thermalconductivity than the manifold 12 a and nozzle 20 a may be used.

FIG. 2 shows the injection molding apparatus 10 a in a cold, ornon-operating, condition, in which the apparatus 10 a is below anoperating temperature. This condition occurs prior to operation of theinjection molding apparatus 10 a. Referring to FIG. 3, the injectionmolding apparatus 10 a is shown in the operating condition, in which thetemperature of the injection molding apparatus 10 a is in an operatingtemperature range. As shown, the sealing insert 44 a has lengthened toremove the cold clearance 48 and impart a sealing force, as indicated byarrows 54, on the outlet surface 28 of the manifold 12 a.

In operation, the injection molding apparatus 10 a starts in the coldcondition of FIG. 2, in which all of the components are at generally thesame ambient temperature. During operation, the manifold 12 a having amanifold channel 14 a and the nozzle 20 a having nozzle channel 22 a areheated and then maintained at their respective temperatures so that themelt stream may flow unhindered into the melt cavity 30 a, which ischilled. The nozzle 20 a and manifold 12 a must maintain tight alignmentwith each other while in the operating temperature range. The manifold12 a and the nozzle 20 a may be subject to different amounts of heatexpansion, particularly if they are comprised of different materials. Inthe injection molding apparatus of FIG. 2, the manifold 12 a is allowedto have a lateral displacement relative to the nozzle 20 a because thenozzle 20 a is not coupled to the manifold 12 a by a fastener.

As the manifold 12 a heats up to operating temperature, the nozzle 20 ais heated by contact with the manifold 12 a and also by heater 40. Dueto heat expansion, the manifold 12 a applies pressure to nozzle 20 a andthe spring 52. At the same time, due to the heat expansion of the nozzle20 a, the nozzle 20 a applies pressure to the outlet surface 28 of themanifold 12 a. As a result, the spring 52 compresses to avoid damage tothe manifold 12 a and nozzle 20 a. The sealing insert 44 a also respondsto the temperature increase by expanding more than the nozzle 20 a andthus applying sealing force to the outlet surface 28 of the manifold 12a. Because the sealing insert 44 a has a high thermal conductivity, thelength 60 of the sealing insert 44 a increases by a larger amount thanthe surrounding components. This is shown by length 60′ in FIG. 3. Thepressure applied to the manifold 12 a by the sealing insert 44 a isgreater than the injection forces generated by the melt stream, whichattempt to push the manifold 12 a and nozzle 20 a apart and create aclearance for the melt stream to leak under pressure.

The spring 52 is relatively stiff and compresses to reduce forces thatmay be large enough to damage the nozzle 20 a or the manifold 12 a. Thespring 52 does not compress due to the sealing force applied by thesealing insert 44 a. Instead, the sealing insert 44 a is designed to atleast partially collapse if the sealing force applied is too large. Thesealing insert 44 a is a relatively inexpensive component and therefore,is easily replaced if damaged.

It will be appreciated by a person skilled in the art that the length 60and wall thickness 62 of the sealing insert 44 a may be varied to suitthe sealing requirements of a particular application.

Turning now to FIG. 4, another embodiment of an injection moldingapparatus 10 b is shown. The injection molding apparatus 10 b is similarto the injection molding apparatus 10 and 10 a of FIG. 1 and FIGS. 2 and3, respectively. A nozzle 20 b includes a shoulder flange 70 thatextends outwardly from a top portion thereof. The shoulder flange 70 iscoupled to a manifold 12 b by a fastener 72. Additional fasteners 72 maybe used, however, for simplicity only one is shown in the Figures.

A manifold plate 36 b abuts a mold cavity plate 35 b of mold cavity 30 band supports the nozzle 20 b. The nozzle 20 b engages mounting elements38, which extend from the inner wall 42 of the manifold plate 36 b, tolocate the nozzle 20 b and manifold 12 b, which is fastened thereto,relative to the mold cavity plate 35 b.

A first recess 41 b having a shoulder 46 b is formed in the uppersurface 26 b of the nozzle 20 b. A second recess 74 having a shoulder 76is formed in an outlet surface 28 b of the manifold 12 b. A sealinginsert 44 b having a bore 47 b is nested in the recess 41 b and extendsbeyond an upper surface 26 b of the nozzle 20 b through a portion ofsecond recess 74. The melt stream flows through bore 47 b of the sealinginsert 44 b from a manifold outlet 18 b to a nozzle channel 22 b.

The sealing insert 44 b has a length 60 b and is generally similar inconstruction to the sealing insert 44 a of FIGS. 2 and 3. The sealinginsert 44 b and manifold 12 b are arranged so that a cold clearance,indicated at 48 b, is provided between the sealing insert 44 b and theshoulder 76 of the manifold 12 b.

In operation, the injection molding apparatus 10 b starts in the coldcondition of FIG. 4 and is heated to the operating condition of FIG. 5,as has been described in relation to FIGS. 2 and 3. As the manifold 12 bhaving a manifold channel 14 b heats up to operating temperature, thenozzle 20 b having a nozzle channel 22 b is heated by contact with themanifold 12 b and also by heaters 40. The fastener 72 typically expandsalong with the manifold 12 b and nozzle 20 b. The expansion of themanifold 12 b and nozzle 20 b assembly is absorbed by spring 52. Gap 51is reduced so that damage to the manifold 12 b and nozzle 20 b isavoided.

At the same time, the sealing insert 44 b expands and applies a sealingforce, in the direction indicated by arrow 54 b, to the manifoldshoulder 76, as is shown in FIG. 5. Because the sealing insert 44 b hasa higher thermal conductivity than both the nozzle 20 b and manifold 12b, the length 60 b of the sealing insert 44 b increases by a largeramount than the surrounding components. This is shown by length 60 b′ inFIG. 5. The pressure applied to the manifold shoulder 76 by the sealinginsert 44 b is greater than the injection forces of the melt stream,which attempt to push the manifold 12 b and nozzle 20 b apart.

The sealing insert 44 b of the injection molding apparatus 10 badditionally allows for location of the nozzle 20 b relative to themanifold 12 b. The sealing insert 44 b projects beyond the upper surface26 b of the nozzle 20 b so that the nozzle channel 20 b can be alignedwith the manifold outlet 18 b.

Turning now to FIGS. 6 and 7, another embodiment of an injection moldingapparatus 10 c is shown. The injection molding apparatus 10 c is similarto the injection molding apparatus 10 b of FIGS. 4 and 5, however, theinjection molding apparatus 10 c incorporates a sealing insert 44 csimilar to sealing insert 44 a of FIGS. 2 and 3. A manifold 12 c havinga manifold channel 14 c is similar to the manifold 12 b of FIGS. 4 and5, however, it has a flat outlet surface 28 c and does not incorporatethe second recess 74. Operation of the embodiment of FIGS. 6 and 7 neednot be described in detail as the sealing action of the sealing insert44 c to reduce leakage between nozzle 20 c and manifold 12 c hasgenerally been described in relation to FIGS. 1-5.

Referring to FIG. 8, a further embodiment of an injection moldingapparatus 10 d is shown in a cold, or non-operating condition. Amanifold 12 d includes a manifold channel 14 d for delivering a meltstream through an outlet 18 d to a nozzle channel 22 d of a nozzle 20 d.A collar 90 is provided between an upper surface 26 d of the nozzle andan outlet surface 28 d of the manifold 12 d. The collar 90 includes ashoulder portion 32 d and a spacing flange portion 34 d.

A manifold plug 80 fits into a bore 82 in the manifold 12 d and formspart of the channel 14 d. The manifold plug 80 is press fit into thebore 82 in a manner that would be apparent to one of ordinary skill inthe art. A cold clearance gap 84 is exists between a lower surface 86 ofthe manifold plug 80 and the outlet surface 28 d of the manifold 12 d.The manifold plug 80 behaves in a similar manner as the sealing insert44 that has been previously described in relation to FIGS. 1-7. Inaddition, the manifold plug 80 is formed of similar materials.

As the manifold 12 d heats up to operating temperature, the manifoldplug 80 lengthens to eliminate the cold clearance gap 84, as shown inFIG. 4, and apply pressure to the nozzle 20 d, via collar 90. Theoperating condition, in which leakage between the manifold 12 d and thecollar 90 is reduced due to the manifold plug 80, is shown in FIG. 9.

FIG. 10 shows a further embodiment of an injection molding apparatus 10f. The injection molding apparatus 10 f is a multi-cavity injectionmolding apparatus having a plurality of nozzles 20 f, which inject meltinto a plurality of mold cavities 30 f. FIG. 10 shows a single nozzle 20f and mold cavity 30 f for simplicity. The injection molding apparatus10 f comprises a manifold 12 f having a manifold channel 14 f extendingtherethrough for receiving a melt stream of moldable material from amachine nozzle (not shown). The melt stream flows through the manifoldchannel 14 f and is delivered to an outlet 18 f of the manifold 12 f.Manifold heaters 15 f are provided in the manifold 12 f to maintain themelt stream at a desired temperature.

A backing plate 50 f is located adjacent the manifold 12 f and is offsetby a gap 51 f. A spring 52 f is provided between the backing plate 50 fand the manifold 12 f.

Nozzle 20 f is located between the manifold 12 f and the mold cavity 30f, which is formed in a mold cavity plate 35 f. Each nozzle 20 fincludes a nozzle channel 22 f for receiving the melt stream from themanifold outlet 18 f and delivering the melt stream to the mold cavity30 f. A mold gate 31 f is provided at the entrance to the mold cavity 30f, adjacent a tip 24 f of the nozzle 20 f. Each nozzle 20 f is providedwith one or more heaters 40 f that help to maintain the melt stream at adesired temperature as it passes through the nozzle 20 f.

A nozzle shoulder 32 f is provided at an upper end of the nozzle 20 f.The nozzle shoulder 32 f includes an upper surface 26 f, which abuts anoutlet surface 28 f of the manifold 12 f. A spacer 34 f is locatedbetween a lower surface of the nozzle shoulder 32 f and a contactsurface 37 of the manifold plate 36 f. The spacer 34 f is made of a lowthermally conductive material such as titanium or ceramic, for example.As would be apparent to one of ordinary skill in the art, spacer 34 fpositions and aligns nozzle 20 f with respect to manifold 12 f and moldcavity 30 f.

A manifold plate 36 f abuts the mold cavity plate 35 f. Cooling channels33 f extend through the manifold plate 36 f adjacent the mold cavity 30f in order to aid in the cooling of melt therein.

The nozzle 20 f includes a recess 41 f that is formed in the uppersurface 26 f, or manifold contacting surface, of the nozzle 20 f. Therecess 41 f is delimited by a shoulder 46 f. A sealing insert 44 fhaving a bore 47 f is nested in the recess 41 f. When the injectionmolding apparatus 10 f is in the cold condition a clearance (not shown)is provided between the sealing insert 44 f and the outlet surface 28 fof the manifold 12 f. The wall thickness of the sealing insert 44 f istypically in the range of 2 to 3 mm.

The sealing insert 44 f has a higher thermal conductivity than both themanifold 12 f and the nozzle 20 f, which are typically comprised of toolsteels such as H13 or P20 steel, for example. The sealing insert 44 fmay be comprised of copper, beryllium copper, brass, carbide or somesteels. Alternatively, any suitable material having a higher thermalconductivity than the manifold 12 f and nozzle 20 f may be used.

In operation, the injection molding apparatus 10 f starts in the coldcondition, in which all of the components are at generally the sameambient temperature. During operation, the manifold 12 f and the nozzle20 f are heated and then maintained at their respective temperatures sothat the melt stream may flow unhindered into the melt cavity 30 f,which is chilled. As the injection molding apparatus 10 f heats up tooperating temperature (shown in FIG. 10) the sealing insert 44 fexpands. Because the sealing insert 44 f has a higher thermal expansioncoefficient, the length of the sealing insert 44 f increases by a largeramount than the surrounding components, including the nozzle 20 f andthe manifold 12 f. As such, the sealing insert 44 f applies a sealingforce to the outlet surface 28 f of the manifold 12 f. The expansion ofthe sealing insert 44 f may, in fact, cause the upper surface 26 f ofthe nozzle 20 f and the outlet surface 28 f of the manifold 12 f to moveapart slightly, however, fluid communication between the components issealed. The bore 47 f of the sealing insert 44 f provides a continuous,sealed path for melt to flow between the manifold outlet 18 f and thenozzle channel 22 f.

A further embodiment of an injection molding apparatus is generallyshown at 10 g of FIG. 11 in which a nozzle 20 g having a nozzle body 104and a nozzle head, or shoulder, 102 is shown. The nozzle head 102operates similarly to the sealing insert 44 of the previous embodimentsby expanding more than the surrounding components to produce a sealbetween manifold channel 14 g of manifold 12 g and nozzle channel 22 g.The nozzle body 104 and nozzle head 102 are coupled together by brazingor a threaded connection, for example (not shown). In this embodiment,the head 102 can be made of different materials than the body 104. Thehead 102 is made of a material having higher thermal conductivity and isheated by manifold 12 g. Spacer 34 g is a separate part that is made ofa material having low thermal conductivity. As would be apparent to oneof ordinary skill in the art, spacer 34 g positions and aligns nozzle 20g with respect to manifold 12 g and mold cavity 30 g.

FIG. 12 shows yet a further embodiment of an injection molding apparatus10 h. In this embodiment a nozzle head 102 h includes a sleeve portion106 that is nested in a recess 41 h provided in a nozzle body 104 h. Thenozzle head 102 h is made of a material having higher thermalconductivity than nozzle body 104 h and is heated by manifold 12 h. Theinjection molding apparatus 10 h is shown in an operating condition andthe nozzle head 102 h exerts a sealing force 54 h in a similar manner asthe sealing inserts 44 of the previous embodiments.

Referring to FIG. 13, a further embodiment of an injection moldingapparatus 10 i is shown. A sealing insert 44 i is mounted in a recess 41i that is formed in an outlet surface 28 i of the manifold 12 i. Therecess 41 i surrounds an outlet 18 i of manifold channel 14 i. Thesealing insert 44 i includes a bore 47 i that is aligned with themanifold channel 14 i to provide a continuous path between manifoldchannel 14 i and nozzle channel 22 i.

A spacer 100 separates the backing plate 50 i and the manifold 12 i. Thespacer 100 is typically comprised of a thermal insulating material suchas titanium or ceramic, for example. The spacer 100 performs a similarfunction as spring 52 of FIG. 2, however, because it is comprised of athermal insulating material, the size of the gap between the manifold 12i and the backing plate 50 i remains generally constant.

The injection molding apparatus 10 i of FIG. 13 is shown in theoperating condition. In this condition, the sealing insert 44 i is in anexpanded state in which the length 60 i of the sealing insert 44 i fillsrecess 41 i and the sealing insert 44 i exerts a sealing force on nozzlehead 102 i of nozzle 20 i. The sealing insert 44 i functions in asimilar manner as the manifold plug 80 of FIGS. 8 and 9, which has beenpreviously described.

A further embodiment of an injection molding apparatus 10 j is shown inFIG. 14. In this embodiment, a manifold 12 j having a manifold channel14 j extending therethrough receives a melt stream of moldable materialfrom a machine nozzle (not shown). Nozzles 20 j are provided adjacentthe manifold 12 j. Each nozzle 20 j includes a nozzle channel 22 j forreceiving the melt stream from a respective manifold outlet 18 j anddelivering the melt stream through a nozzle tip (not shown) to arespective mold cavity (not shown). Each nozzle 20 j is further providedwith a heater 40 j that is coupled to a connector 43. The heater 40 jhelps to maintain the melt stream at a desired temperature as it passesthrough the nozzle 20 j.

The manifold 12 j includes a recess 41 j that is formed in the outletsurface 28 j of the manifold 12 j. The recess 41 j is stepped andincludes a first threaded portion 110 and a first generally smoothportion 112. The recess 41 j is sized to receive a sealing insert 44 j.The sealing insert 44 j, which is shown in FIGS. 15 and 16, includes afirst end surface 114, a second end surface 116 and a bore 47 j thatextends therethrough. An outer surface 118 of the sealing insert 44 jincludes a neck 120 that is provided between a second threaded portion122 and a second generally smooth portion 124. The second threadedportion 122 of the sealing insert 44 j is sized to mate with the firstthreaded portion 110 of the recess 41 j to secure the sealing insert 44j to the manifold 12 j. As shown, the sealing insert 44 j furtherincludes a pair of tooling apertures 126 (only one tooling apertureshown in FIG. 15) that are formed in the second end surface 116 thereofto allow for installation.

The sealing insert 44 j and manifold 12 j are arranged so that a coldclearance is provided between the sealing insert 44 j and a matingsurface 26 j of the nozzle 20 j. The sealing insert 44 j is comprised ofa material having a higher thermal conductivity than both the manifold12 j and the nozzle 20 j. The sealing insert 44 j may be comprised ofcopper, beryllium copper, brass, carbide or some steels. Any suitablematerial having a higher thermal conductivity than the manifold 12 j andnozzle 20 j may be used. The wall thickness of the sealing insert 44 jis typically in the range of 2 to 4 mm.

In operation, the injection molding apparatus 10 j starts in a coldcondition, in which all of the components are at generally the sameambient temperature. During operation, the manifold 12 j and the nozzle20 j are heated and then maintained at their respective temperatures sothat the melt stream may flow unhindered into the melt cavity. Theheated, or operating, condition is shown in FIG. 14. The sealing insert44 j responds to the temperature increase by expanding more than themanifold 12 j and thus applying sealing force to the mating surface 26 jof the nozzle 20 j. Because the sealing insert 44 j has a high thermalconductivity, the length 60 j of the sealing insert 44 j increases by alarger amount than the surrounding components. The pressure applied tothe nozzle 20 j by the sealing insert 44 j is greater than the injectionforces generated by the melt stream, which attempt to push the sealinginsert 44 j and the nozzle 20 j apart and create a clearance for themelt stream to leak under pressure.

Although preferred embodiments of the present invention have beendescribed, those of skill in the art will appreciate that variations andmodifications may be made without departing from the spirit and scopethereof as defined by the appended claims.

1. An injection molding apparatus comprising: a manifold having amanifold channel, said manifold channel having an inlet for receiving amelt stream of moldable material and an outlet for delivering said meltstream to a nozzle channel of a nozzle; a sealing element providedbetween said nozzle and said manifold such that an upstream surface ofsaid sealing element extends beyond an upstream surface of said nozzlein a cold condition, said sealing element including a melt channel forreceiving said melt stream from said outlet of said manifold channel anddelivering said melt stream to said nozzle channel; and a mold cavityfor receiving said melt stream from said nozzle channel, said nozzlechannel communicating with said mold cavity; wherein said sealingelement has a higher thermal expansion coefficient than both said nozzleand said manifold.
 2. An injection molding apparatus as claimed in claim1, wherein a recess is formed in the upstream surface of said nozzle,said recess being sized to receive said sealing element.
 3. An injectionmolding apparatus as claimed in claim 2, wherein said melt channel ofsaid sealing element provides a continuous path between said nozzlechannel and said outlet of said manifold.
 4. An injection moldingapparatus as claimed in claim 1, wherein said sealing element abuts saidmanifold at an operating temperature to provide a seal between saidsealing element and said manifold.
 5. An injection molding apparatus asclaimed in claim 4, wherein said sealing element is comprised of copper.6. An injection molding apparatus as claimed in claim 4, wherein saidsealing element is comprised of beryllium copper.
 7. An injectionmolding apparatus as claimed in claim 4, wherein said sealing element iscomprised of brass.
 8. An injection molding apparatus as claimed inclaim 1, wherein a first recess is provided in an outlet surface of saidmanifold and a second recess is provided in the upstream surface of saidnozzle, said first recess and said second recess being aligned toreceive said sealing element.
 9. An injection molding apparatus asclaimed in claim 8, wherein in a cold condition, a clearance is providedbetween said sealing element and an offset surface of said first recess.10. An injection molding apparatus as claimed in claim 9, wherein at anoperating temperature said sealing element abuts said offset surface ofsaid first recess to provide a seal between said sealing element andsaid manifold.
 11. An injection molding apparatus as claimed in claim10, wherein said sealing element is comprised of copper.
 12. Aninjection molding apparatus as claimed in claim 10, wherein said sealingelement is comprised of beryllium copper.
 13. An injection moldingapparatus as claimed in claim 10, wherein said sealing element iscomprised of brass.
 14. An injection molding apparatus comprising: amanifold having a manifold channel; a nozzle having a nozzle channel influid communication with said manifold channel; a sealing elementprovided between said nozzle and said manifold, said sealing elementincluding a melt channel in fluid communication with said manifoldchannel and said nozzle channel; wherein said manifold includes a firstrecess provided in an outlet surface thereof for receiving said sealingelement, said melt channel of said sealing element being aligned withsaid nozzle channel and said manifold channel; and wherein said sealingelement has a higher thermal expansion coefficient than both said nozzleand said manifold.
 15. An injection molding apparatus as claimed inclaim 14, wherein in a cold condition a clearance is provided between amanifold contacting surface of said nozzle and said sealing element. 16.An injection molding apparatus as claimed in claim 15, wherein in anoperating condition a seal is provided between said sealing element andan upstream surface of said nozzle.
 17. An injection molding apparatusas claimed in claim 16, wherein said sealing element is comprised ofcopper.
 18. An injection molding apparatus as claimed in claim 16,wherein said sealing element is comprised of beryllium copper.
 19. Aninjection molding apparatus as claimed in claim 16, wherein said sealingelement is comprised of brass.
 20. An injection molding apparatus asclaimed in claim 15, wherein said sealing element includes threadslocated on at least a portion of an outer surface thereof, said threadsof said sealing element for mating with a threaded inner surface of saidfirst recess.
 21. An injection molding apparatus comprising: a manifoldhaving a manifold channel for receiving a melt stream of moldablematerial under pressure; a manifold plug provided in said manifold, saidmanifold plug having a manifold plug channel formed therein, saidmanifold plug channel having an inlet for receiving said melt streamfrom said manifold channel and an outlet for delivering said melt streamto a nozzle channel of a nozzle; and a mold cavity for receiving saidmelt stream from said nozzle channel, said nozzle channel communicatingwith said mold cavity through a mold gate; wherein said manifold plughas a higher thermal expansion coefficient than both said nozzle andsaid manifold.
 22. An injection molding apparatus as claimed in claim21, wherein in a cold condition, a clearance is provided between a loweredge of said manifold plug and a manifold contacting surface of saidnozzle.
 23. An injection molding apparatus as claimed in claim 22,wherein in an operating condition said manifold plug abuts said manifoldcontacting surface of said nozzle to provide a seal between saidmanifold plug and said nozzle.
 24. An injection molding apparatus asclaimed in claim 23, wherein said manifold plug is comprised of copper.25. An injection molding apparatus as claimed in claim 23, wherein saidmanifold plug is comprised of beryllium copper.
 26. An injection moldingapparatus as claimed in claim 23, wherein said manifold plug iscomprised of brass.
 27. An injection molding apparatus comprising: amanifold having a manifold channel, said manifold channel having aninlet for receiving a melt stream of moldable material under pressureand an outlet; a nozzle having a nozzle body and a nozzle head, saidnozzle head being located adjacent an outlet surface of said manifold,said nozzle having a nozzle channel for receiving said melt stream fromsaid outlet of said manifold channel; and a mold cavity for receivingsaid melt stream from said nozzle channel, said nozzle channelcommunicating with said mold cavity through a mold gate; wherein atleast a portion of said nozzle head has a higher thermal expansioncoefficient than both said nozzle body and said manifold.
 28. Aninjection molding apparatus as claimed in claim 27, wherein in a coldcondition a clearance is provided between said nozzle head and an outletsurface of said manifold.
 29. An injection molding apparatus as claimedin claim 28, wherein in an operating condition said nozzle head abutssaid outlet surface of said manifold to provide a seal between saidnozzle head and said manifold.
 30. An injection molding apparatus asclaimed in claim 29, wherein said nozzle head is integral with saidnozzle body.